The present invention relates to the dispensing and delivery of liquids. In particular, the present invention relates to a system for dispensing liquid that allows for easy control of the volume and speed of liquid dispensed from the same input liquid source.
Certain manufacturing processes require the use of liquid chemicals such as acids, solvents, bases, photoresists, dopants, inorganic solutions, organic solutions, biological solutions, pharmaceuticals, and radioactive chemicals. In many manufacturing process applications, fluid containers are employed as a source of process liquids for liquid delivery systems. Typically, the fluid containers are fabricated and filled at locations remote from the end-use facility. After filling the containers at a filling facility, the containers are typically shipped to the end-use facility, such as for use in a manufacturing process.
At the end-use facility, the fluid container is either incorporated directly into a liquid dispensing system or the liquid from the fluid container is emptied directly into a reservoir connected to the liquid delivery system. Liquid dispensing systems allow alternative containers to be used to deliver liquid chemicals to a manufacturing process at a specified time. These process liquids are usually dispensed from the fluid containers by special dispensing pumps.
In the manufacture of thin film transistor flat panel displays, the dispensing and delivery of many expensive chemicals is required. These chemicals include photoresist, color filter material, black matrix material, and so on. These chemicals are typically dispensed in the manufacturing process for spin coating, slit/extrusion coating, or a combination of the two. Systems that dispense these chemicals must be flexible to allow for different amounts of chemical and different dispense speeds to be realized with the same chemical input. Systems incapable of serving this function necessitate redundant dispense equipment, thereby increasing the overall cost of the system.
Most current dispensing systems that allow for different amounts of chemical and different dispense speeds to be realized with the same input liquid source employ dispense pumps in the dispense train. These pumps are not only expensive, but also are known to contribute to contamination in the form of bellows and diaphragm shedding, as well as shedding from wear on the pump check valves. Some systems attempt to engineer around the expensive pumps with an arrangement wherein the liquid is forced out of the container with a drive gas. However, the accuracy and flexibility of the amount and speed of chemical dispensed are difficult to maintain. Further, the drive gas can be forced into the dispensed liquid, thereby causing microbubbles to form in the liquid. The presence of microbubbles in the deposited liquids may cause defects in the deposited layer or subsequent deposited layers.
Another conventional approach to varying the amount and speed of chemical dispensed from the same input liquid source involves using a flow control device in the dispense train. In this type of system, flow rate is controlled via a closed feedback loop, and the volume of the dispense is controlled by the amount of time the liquid is dispensed. However, some dispensing systems using flow control devices have poor stability when a certain amount of liquid must be dispensed in a short period of time. Also, flow control devices are very expensive, thus adding to the overall cost of the dispense system.
Thus, there is a need for a low-cost liquid dispensing system that eliminates the use of pumps and allows for easy control of the amount and speed of fluid dispensed from the same input fluid source.